Densities and Viscosities of Aqueous Alkaline ... - ACS Publications

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Densities and Viscosities of Aqueous Alkaline Nitrate and Nitrite Solutions Used in Absorption Heat Pumps Gorg Abdelmassih* and Xavier Esteve§ Department of Mechanical Engineering, Rovira i Virgili University, 26 Paisos Catalans Street, 43007, Tarragona, Spain ABSTRACT: Density and dynamic viscosity of four aqueous alkaline nitrate and nitrite solutions were measured experimentally. These considered solutions are used in developed absorption refrigeration cycles and heat pumps as binary working fluids (coolant/absorber). Experimentations used a vibrating-tube densimeter and piston-style viscosimeter for density and viscosity, respectively. The measurements were accomplished at atmospheric pressure. Two solutions (salts/ water) were made of lithium nitrate, potassium nitrate, and sodium nitrate (LiNO3 + KNO3 + NaNO3) in the mass ratios of 53:28:19 and 53:42:5. The other two solutions of salts with water were lithium nitrate, potassium nitrate, and sodium nitrite (LiNO3 + KNO3 + NaNO2) in salt mass ratios of 53:35:12 and 60:36:4. These compositions were selected according to the best solubility. In the experimental study, the salt mass fraction was varied from 0.50 to 0.80. On the other hand, the temperature range adopted is from (323.15 to 403.15) K. Also some mathematical models were used to predict the values of the experimental values for comparison. The models resulted in very good agreement with the experimental results.

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INTRODUCTION During the last decades the increase in energy consumption around the world has forced research of alternative energy sources and optimization of existing resources. This new research should take into consideration the impact on the environment since increasing the energy consumption implies a series of negative climate changes as well as growth of the hole in the ozone layer. Technological development and energy efficiency were the solution keys of such a problem. For this reason, absorption cycles became of more interest than the traditional systems powered by electricity and vapor compression cycles in the cooling aspects. The first applications of absorption refrigeration cycles were in the second half of the 19th century, and even experienced a remarkable boom in the first half of the twentieth century. The use of absorption systems was motivated after the late 1980s because of more stringent environmental regulations as for the traditional refrigerants. These systems are attractive alternatives for both domestic and industrial applications. In the late 1980s and early 1990s, due to the high price of electricity, installation of cogeneration plants in industry and in the tertiary sector was promoted. The available waste heat was used in many cases to operate a water-cooling lithium bromide air conditioner, or ammonia−water systems in the case of cooling. The commercial working fluids in these absorption cycles are mixtures of (coolant/absorber) lithium bromide/water (LiBr + H2O) or ammonia/water (NH3 + H2O). Each of both mixtures has a number of constraints, such as corrosion, the crystallization of salt, and a 279 K minimum operating temperature for the LiBr + H2O mixture. These constraints © XXXX American Chemical Society

would also include the relatively high volatility of absorbing water, which undertakes to rectify the process steam generator output to reduce the presence of water in this steam, besides the technical difficulty posed by the use of correction in the case of using NH3 + H2O. In 80 years, Davidson and Erickson1,2 patented the use of aqueous solutions of alkali nitrates and nitritesto be used as working fluids in absorption heat pumps at high temperature up to 533.15 K, and they called it Alkitrate. Lithium nitrate has a high specific heat and a high absorption capacity; thus this component is qualified to be used as an absorbent. However, it has a relative high crystallization temperature which implies a very low solubility in water. For this reason the addition of nitrate and/or alkali nitrites not only improves the solubility of the salt but also other characteristics of the mixture are thus improved. The proposed aqueous mixture consisted of lithium nitrate, potassium nitrate, and sodium nitrate (LiNO3 + KNO3 + NaNO3) (53:28:19, Table 1. Sample Information: Salts chemical name

chemical formula

source

mole fraction purity

lithium nitrate sodium nitrate potassium nitrate lithium nitrite

LiNO3 KNO3 NaNO3 NaNO2

Fluka Panreac Panreac Aldrich

0.99 0.99 0.99 0.99

Received: April 10, 2015 Accepted: July 14, 2015

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DOI: 10.1021/acs.jced.5b00103 J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

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Figure 1. Sketch of the equipment used for the density and the viscosity measurements.

Table 3. Continued

Table 2. Sample Information: Sample Solutions samples a

solution 1

solution 2 solution 3b solution 4

ternary salt

salt mass ratio

salt mass fraction

LiNO3 + KNO3 + NaNO3 LiNO3 + KNO3 + NaNO3 LiNO3 + KNO3 + NaNO2 LiNO3 + KNO3 + NaNO2

53:28:19, weight percent 53:42:5, weight percent 53:35:12, weight percent 60:36:4, weight percent

(50, 60, 70, 75 and 80) % (50, 60, 70, 75 and 80) % (50, 60, 70, 75 and 80) % (50, 60, 70, 75 and 80) %

ρ/(kg·m−3)

T/K

a Solution 1 is the Davidson and Erickson’s working pair2 bSolution 3 is the Vargas et al.12 working pair.

Table 3. Experimental Results of Density ρ at Temperature T and Salt Mass Fraction W for the Aqueous Mixturesa ρ/(kg·m−3)

T/K

LiNO3 + KNO3 + NaNO3




(53:28:19)

(53:42:5)

(53:35:12)

(60:36:4)

1349.69 1341.88 1334.33 1326.99 1319.89 1312.96 1306.21 1299.54 1292.97

1352.21 1344.57 1336.69 1328.96 1321.65 1314.56 1307.78 1301.07 1294.44

1444.76 1436.82 1429.06 1421.51 1414.03 1406.79 1399.91 1393.27

1442.03 1434.08 1426.62 1419.53 1412.03 1404.82 1397.91 1391.19

323.54 333.41 343.30 353.33 363.38 373.30 383.25 393.33 403.48

1355.58 1347.65 1340.04 1332.50 1325.12 1317.99 1311.09 1304.34 1297.63

333.31 343.19 353.19 363.14 373.10 383.15 393.18 403.42

1448.79 1440.76 1432.89 1425.31 1418.00 1410.70 1403.87 1397.00

W = 0.5 1353.65 1345.93 1338.45 1331.04 1323.45 1316.17 1309.14 1302.36 1295.68 W = 0.6 1449.12 1441.21 1433.22 1425.41 1417.99 1410.97 1404.07 1397.77





(53:28:19)

(53:42:5)

(53:35:12)

(60:36:4)

1547.62 1538.99 1531.22 1523.76 1516.64 1509.75 1503.38

1546.06 1537.61 1529.56 1522.03 1514.93 1507.98 1501.26

1589.43 1581.79 1574.58 1567.6 1560.78

1590.03 1582.38 1575.24 1568.16 1561.34

1655.4 1651.47 1647.63 1640.44 1633.72 1627.24

1655.37 1651.3 1647.46 1640.03 1632.84 1625.84

343.28 353.29 363.39 373.31 383.26 393.29 403.45

1553.05 1544.67 1536.51 1528.86 1521.62 1514.56 1507.64

363.74 373.64 383.53 393.48 403.46

1599.19 1591.55 1584.31 1577.36 1570.57

363.12 368.06 373.09 383.23 393.32 403.08

1670.08 1666.17 1662.27 1654.58 1647.24 1640.98

W = 0.7 1551.49 1543.13 1534.83 1527.17 1519.97 1513.04 1506.2 W = 0.75 1597.71 1589.75 1582.39 1575.33 1568.42 W = 0.8 1653.06 1649.39 1645.68 1631.74 1621.64 1613.64

a LiNO3, lithium nitrate; KNO3, potassium nitrate; NaNO3, sodium nitrate; NaNO2, sodium nitrite; H2O, water; W, salt mass fraction in the salts/water solutions. Standard uncertainties u are u(T) = 0.01 K, u(W) = 0.001, and the combined expanded uncertainties Uc are Uc(ρ) = 0.01 kg·m−3.

weight percent)2 as the best mix of solubility, without problems of corrosion and thermal stability. Shortly after, Ally3,4 conducted initial studies for the solutions of the ternary mixture using this working fluid for heat pump applications. It has been found that the COP (coefficient of performance) of this fluid mixture is improved in comparison with the conventional water−lithium bromide; as well, the new mixture is a relatively inexpensive B



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to achieve this study. The purpose of this work is to increase the awareness of aqueous mixtures of alkali nitrates and nitrites to establish the feasibility of absorption refrigeration systems based on multiuse of these mixtures which are eligible to be activated to direct flame. These systems also allow better energy efficiency compared to other refrigeration systems for absorption. To carry out the simulation and analysis of thermodynamic cycles of multiabsorption, it was necessary to know accurately the solubility,12 the vapor−liquid equilibrium,13 the heat capacity, density, and viscosity of aqueous mixtures at operating conditions cycle. It will be necessary to have the properties of the working fluid at different temperatures for different concentrations, allowing the modeling of alkaline aqueous systems alkali nitrates/nitrites. Thus, the aim of this paper is presenting experimental results of two of the thermophysical properties, density and viscosity, which are essential to study the transport phenomena of the salt solutions proposed. The density of the fluids used in the absorption systems is very important in the design of the equipment. It is common to use

absorbent. Afterward, several studies were performed to study the different aspects of thermo-physical properties of the mixture in different absorption cycles configurations.5−10 Although all of these are good characteristics, the mixture of interest cannot be cooled to ambient temperatures because of the crystallization problem which restricted the use of the mixture in low temperatures and pressures conditions. For this reason, it was recommended elsewhere7,11 that the Alkitrate mixture be used merely during the high-temperature stages of absorption cycles. Vargas et al.12 reported that the highest solubility is in a mixture of H2O/(LiNO3 + KNO3 + NaNO2) for which the relative absorbent weight percentage is 53:35:12. Alvarez et al.13 achieved vapor−liquid equilibrium measurements for the working pairs mentioned in previous studies.2,12 This study was accomplished using a static method in the temperature range (333.15 to 473.15) K at 20 K intervals. The salt mass fraction varied from 0.50 to 0.95. However, the shortage of information currently available in the literature about the transport properties of aqueous alkaline, nitrate, and nitrite solutions was the main cause

Figure 2. Experimental results of density ρ with the temperature T for the salts solutions of LiNO3 + KNO3 + NaNO3 in the mass percent 53:28:19. The salt mass fractions in the solutions are ∗, W = 0.50; ○, W = 0.60; □, W = 0.70; △, W = 0.75; +, W = 0.80.

Figure 3. Comparison between the densities of the salt solutions at the same temperature and mass concentration. The salt solutions of LiNO3 + KNO3 + NaNO3 in the mass percent *, 53:28:19; ○, 53:42:05; and Salt solutions of LiNO3 + KNO3 + NaNO2 □, 53:35:12; ..., 60:36:04. C



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Table 4. Experimental Results of Dynamic Viscosity η at Temperature T and Salt Mass Fraction W for the Aqueous Mixturesa

the density for the sizing of pipes, pumps and also for heat transfer calculations. Furthermore, it is necessary to know the solution concentration at the outlet of the absorber to control the absorption process. In the industrial field viscosity also is critical to the circuit design of fluid systems such as absorption as it is playing an important role in determining the heat and mass transfer. Very few results exist in the literature referring to these two properties for our interested mixtures. The experimental values of Alkitrate solutions density available in the literature are reduced to those presented by Ally et al.6 where experimental data are collected from density and refractive index in a range of temperatures from (298.15 to 473.15) K and concentrations between 0.19 and 0.90 in total mass fraction of the mixture of salts. Also, for the viscosity property the known reference of the Alkitrate solutions of Davidson and Ericsson’s alkitrates is limited to Zaltash et al.8 in which only 13 experimental values are collected for mass fractions between 0.58 and 0.90 and temperatures from (380 to 440) K. In the present work, experimental measurements of the density and viscosity have been accomplished for four alkaline nitrates and nitrite solutions of interests for absorption heat pumps and refrigeration cycles driven by high-temperature heat sources. Two solutions (salts + water) were made of lithium nitrate, potassium nitrate, and sodium nitrate (LiNO3 + KNO3 + NaNO3) in the mass ratios of 53:28:19 and 53:42:5. The other two solutions of salts with water were lithium nitrate, potassium nitrate, and sodium nitrite (LiNO3+ KNO3+ NaNO2) in salt mass ratios of 53:35:12 and 60:36:4. The salt mass fraction was varied from 0.50 to 0.80. These compositions were selected according to the best solubility presented in ref 12. On the other hand, the temperature range adopted is from (323.15 to 403.15) K. The obtained experimental results are fitted by a simulation results obtained using different models of prediction for each property. Most thermodynamic models used to predict the density of electrolyte solutions are based on calculating the molar volume of each of the electrolytes in the mixture and adding these to the molar volume of water. The inverse of this sum is the density of the mixture. Therefore, to develop an appropriate model for a concrete mixture, experimental information is needed for the various components of the same individual, that is, to know the density of aqueous solutions of each of the individual components of the mixture. The process simulator Aspen Properties has integrated the thermodynamic model of Clarke19 for electrolyte solutions. In addition it will examine the application of another thermodynamic model proposed by Laliberte et al.,20 whereas the Hole model8 has been used for the prediction of viscosity.

η/(mPa·s)

T/K





(53:28:19)

(53:42:5)

(53:35:12)

(60:36:4)

1.96 1.65 1.40 1.19 1.06 0.92 0.83 0.74

1.57 1.31 1.12 0.97 0.84 0.74 0.65 0.58

3.23 2.71 2.18 1.84 1.63 1.38 1.28

3.02 2.48 1.79 1.51 1.30 1.13 0.99

4.44 3.69 3.40 2.33 2.05 1.87

4.21 3.52 3.06 2.45 2.31 1.75

4.57 3.88 3.41 2.94 2.53

4.58 3.95 3.39 2.92 2.52

6.30 5.86 5.48 4.68 4.03 3.74

5.88 5.45 5.11 4.37 3.83 3.55

333.63 343.51 353.07 362.96 373.15 382.69 392.88 402.44

2.11 1.84 1.56 1.33 1.29 1.26 0.92 0.95

333.92 343.75 363.23 373.19 383.10 393.00 403.01

2.91 2.54 1.90 1.63 1.41 1.24 1.09

343.88 353.44 363.44 383.26 393.14 403.07

4.11 3.41 2.86 2.22 1.93 1.69

363.51 373.39 383.28 393.14 402.93

3.89 3.61 2.91 2.57 2.28

363.13 368.12 373.11 383.21 393.23 402.79

6.18 5.80 5.45 4.63 4.09 3.84

W = 0.50 1.68 1.43 1.24 1.06 0.94 0.83 0.73 0.65 W = 0.60 2.66 2.25 1.67 1.45 1.27 1.13 1.07 W = 0.70 4.05 3.44 2.81 2.21 1.97 1.72 W = 0.75 4.11 3.56 3.11 2.71 2.39 W = 0.80 5.48 5.19 4.72 4.13 3.63 3.32

a

LiNO3, lithium nitrate; KNO3, potassium nitrate; NaNO3, sodium nitrate; NaNO2, sodium nitrite; H2O, water; W, salt mass fraction in the salts/water solutions. Standard uncertainties u are u(T) = 0.01 K, u(W) = 0.001, and the combined expanded uncertainties Uc are Uc(η) = 0.01 mPa·s.

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EXPERIMENTAL SETUP Materials and Samples. The salts used in preparing the binary solution are listed in the sample information in Table 1. Before preparing the samples, the salts were dried in a vacuum furnace at 393.15 K for 2 days. The salts were used without further purification. Apparatus and Experimental Procedure. The experimental equipment, which is schematically shown in Figure 1, consists of an Anton-Paar densimeter connected with a pistonstyle viscosimeter, pressure regulator, pressure translator, JULABO thermal bath, and vacuum pump. All these devices are under control of a computer program. The experimental instrumentation, calibration, and procedures used have already been described in the previous studies.14−17

The densities were measured using an Anton-Paar vibratingtube densimeter (DMA 60/512P) with an accuracy of ± 0.1 kg·m−3. The instrument model is connected to a pressure system. The measurements are taken in the temperature range between (323.15 and 403.15) K. As a consequence, the vibrating-tube densimeter is thermostated using a water-bath during the measurements. The water-bath used was JULABO, model F20-ME, with a resolution of 0.1 K. The temperature of the samples was measured using a digital precision thermometer (Anton-Paar MKT100) with an accuracy of ± 0.01 K. The Anton-Paar densimeter uses an oscillating U-tube to determine D



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Figure 4. Experimental dynamic viscosity η with the temperature T for the salt solutions of LiNO3 + KNO3 + NaNO2 in the mass percent (60:36:04). The salt mass fractions in the solutions are ∗, W = 0.50; ○, W = 0.60; □, W = 0.70; △, W = 0.75; +, W = 0.80.

the mass percent 53:28:19 with different mass fractions. It is obvious that the density decreases with the temperature, and increases with total salt concentration; that is, the density is a function of temperature and concentration. The data obtained for the density of the four aqueous mixtures tested show similar tendencies to that shown in Figure 2. A comparison between the four mixtures densities under the same conditions is demonstrated in Figure 3. The results illustrate that the density differences between the four aqueous alkaline nitrate and nitrite solutions, at the same temperature and total mass concentration, are less than 1.7 %. Two thermodynamic models for predicting the density were used to evaluate the experimental results: a model of Clarke,19 that is, using Aspen Properties, and model Laliberte and Cooper.20 The quality of these models is compared with the experimental values proposed by Ally et al.6 The models resulted in very good agreement with the experimental results. The rootmean-square relative deviation (RMSD) has been calculated according to eq 1:

the density. This technique is based on an electronic measurement of the frequency of oscillation, from which the density value is calculated. The calibration validity was performed by measuring the density of pure water in the temperature range from (283.15 to 353.15) K. The average deviation between the measured data and the data from the literature18 was 0.18 %. The dynamic viscosities of the solutions were measured using a piston-style viscosimeter (SPL 372, Cambridge). It consists of a 316 stainless steel sensor which is magnetically forced by two magnetic coils to move across a chamber filled with the fluid sample. The time required for the piston to complete a two-way cycle between the coils is an accurate measure of viscosity of the fluid sample. In this study, a piston with a viscosity range of (1 to 20) mPa·s is used. The samples are thermostated with the same water-bath used for the density measurements, and sample temperatures are measured with a thermometer (Pt-100) located inside the viscosimeter. The viscosimeter system is calibrated in the factory and validated using two viscosity reference standards (types N10 and N26).17 Relative deviation is less than 1 %. The solutions were prepared accurately by preparing the ternary salt at first. The salts were carefully weighed using a Mettler electronic scale with a resolution of 1.0 mg to obtain the desired concentration. Second, the corresponding amount of water was added according to the salt mass fraction of each sample. The solutions are prepared using Millipore water (resistivity < 18.2 MΩ). Then, the obtained solution was stirred by a magnetic needle driven by a variable-speed electric motor. Before the injections of the samples, the equipment was cleaned and evacuated by heating for a few hours to remove the residual humidity. The Sample solutions studied in this work are shown in Table 2.

⎡ 1 RMSD = 100⎢ ⎢⎣ N

⎛ Xe − Xc/b ⎞2 ⎤ ⎟⎥ ∑⎜ Xe ⎠i ⎥⎦ i ⎝

1/2

(1)

where N, Xe, and Xc/b are the number of data points, and the experimental and calculated (or the bibliographic) values, respectively. The RMSD values were less than 0.55 % for all substances of the four mixtures. The dynamic viscosities of the four aqueous alkaline nitrate and nitrite solutions were measured at the atmospheric pressure. The temperature range is from (333.15 to 403.15) K. The salt mass fraction was varied from 0.50 to 0.80. Table 4 shows the dynamic viscosity data for the four aqueous alkaline nitrate and nitrite solutions studied. The experimental results of the dynamic viscosity with the temperature for the aqueous mixture of LiNO3 + KNO3 + NaNO2 in the mass percent 60:36:4 with different mass fractions are shown in Figure 4. The performance of the viscosity with the temperature of the four aqueous mixtures tested show similar tendencies. The results show that the dynamic viscosity decreases with temperature and increases with the

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RESULTS AND DISCUSSION The densities of the aqueous alkaline nitrate and nitrite solutions are determined at atmospheric pressure, temperatures ranging from (323.15 to 403.15) K, and salt mass fractions of between 0.50 and 0.80. The experimental data-points of the measured densities are reported in Table 3. Figure 2 shows the experimental results of the density with the temperature for the salt solution of LiNO3 + KNO3 + NaNO3 in E



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Figure 5. Comparison between the dynamic viscosities of the salt solutions at the same temperature and mass concentration. The salt solutions of LiNO3 + KNO3 + NaNO3 in the mass percent *, 53:28:19; ○, 53:42:05; and Salt solutions of LiNO3 + KNO3 + NaNO2 □, 53:35:12; ..., 60:36:04.

Figure 6. Comparison between the experimental and predicted viscosities for the salt solutions: ∗, experimental viscosities at w = 0.50; +, experimental viscosities at w = 0.60; □, experimental viscosities at w = 0.70; △, experimental viscosities at w = 0.75; ..○.., predicted viscosities by Hole model.8

salt concentration for all of these fluid mixtures, which implies that the viscosity is a function of temperature and concentration also. A comparison between the viscosities of the four mixtures is shown in Figure 5, to reveal the viscosity differences between the four aqueous alkaline nitrate and nitrite solutions, at the same temperature and total mass concentration. The viscosity differences are found to be within approximately 20 %. The viscosity values obtained for the LiNO3 + KNO3 + NaNO2 aqueous solution with salt mass ratios of 53:35:12 are higher than the rest of the aqueous solutions for all cases of mass fractions except for the salt mass fraction of 0.50 at which the viscosity of aqueous solution LiNO3 + KNO3 + NaNO3 with salt mass ratios of 53:28:19 is the highest. Although, the viscosity is almost independent of pressure variations in a wide range, it is shown in our study that the effect

of temperature on the relative viscosity is small at low concentrations, whereas for high concentrations, the influence of temperature is significant. The thermodynamic models used for viscosity prediction are more complex than in the case of density prediction. There exist some theoretical models, very complicated and difficult to apply to electrolytic systems, while other semiempirical models, in which some parameters are derived from experimental data, are less accurate than their predecessors. However, for the specific case of the mixtures under study, Zaltash et al.8 proposed the use of a Hole model for the prediction of viscosity; as well, Aspen Properties includes a series of models based on the Jones−Dole equation, a priori applicable to our aqueous mixtures of Alkitrates. Figure 6 shows a comparison between the experimental and predicted viscosities by the Hole model8 of the four solutions understudy at the same condition of temperature and mass F



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(11) Erickson, D.; Howe, L. Development of a High Temperature Absorption Working Pair. Winter Annu. Meet. Am. Soc. Mech. Eng. 1989, 47−53. (12) Vargas, P.; Salavera, D.; Galleguillos, R.; Coronas, A. Solubility of Aqueous Mixtures of Alkaline Nitrates and Nitrites Determined by Differential Scanning Calorimetry. J. Chem. Eng. Data 2008, 53, 403− 406. (13) Á lvarez, M.; Bourouis, M.; Esteve, X. Vapor-Liquid Equilibrium of Aqueous Alkaline Nitrate and Nitrite Solutions for Absorption Refrigeration Cycles with High-Temperature Driving Heat. J. Chem. Eng. Data 2011, 56, 491−496. (14) Esteve, X.; Conesa, A.; Coronas, A. Liquid Densities, Kinematic Viscosities, and Heat Capacities of Some Alkylene Glycol Dialkyl Ethers. J. Chem. Eng. Data 2003, 48, 392−397. (15) Salavera, D.; Esteve, X.; Patil, K.; Mainar, A.; Coronas, A. Solubility, Heat Capacity, and Density of Lithium Bromide + Lithium Iodide + Lithium Nitrate + Lithium Chloride Aqueous Solutions at Several Compositions and Temperatures. J. Chem. Eng. Data 2004, 49, 613−619. (16) Salavera, D.; Libotean, S.; Patil, K.; Esteve, X.; Coronas, A. Densities and Heat Capacities of the Ammonia + Water + NaOH and Ammonia + Water + KOH Solutions. J. Chem. Eng. Data 2006, 51, 1020−1025. (17) Libotean, S.; Martín, A.; Salavera, D.; Vallès, M.; Esteve, X.; Coronas, A. Densities, Viscosities, and Heat Capacities of Ammonia + Lithium Nitrate and Ammonia + Lithium Nitrate + Water Solutions between (293.15 and 353.15) K. J. Chem. Eng. Data 2008, 53, 2383− 2388. (18) Schmidt, E.; Grigull, U. Properties of Water and Steam in SI-Units; Springer-Verlag Berlin Heidelberg: New York, 1981. (19) Chen, C.-C.; Boston, J. F.; Britt, H. I.; Clarke, W. M. Thermodynamic Property Evaluation in Computerized Process Design Scheme for Aqueous Electrolyte Systems. AIChE Symposium Series, No. 229, 1983; Vol. 79, pp 126−134. (20) Laliberté, M.; Cooper, W. Model for Calculating the Density of Aqueous Electrolyte Solutions. J. Chem. Eng. Data 2004, 49, 1141− 1151.

concentration of each case. By comparing the results obtained by this model with the experimental results achieved, the rootmean-square deviation is less than 2.03 %.

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CONCLUSIONS In this work, densities and viscosities of aqueous alkaline nitrate and nitrite solutions used in absorption heat pumps were measured experimentally. It was found that both density and viscosity decrease with the temperature, and increase with total salt concentration. The results of density and viscosity of the tested solutions show similar tendencies for each property. The effect of temperature on the relative viscosity is small at low concentrations whereas for high concentrations, the influence of temperature is rather significant. The experimental results were compared with a simulation results predicted using different models. The models resulted in very good agreement with the experimental results.

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AUTHOR INFORMATION

Corresponding Author

*Fax: +34 977 559 602. E-mail: [email protected]. Funding

This study is part of an R&D project funded by the Spanish Ministry of Science and Innovation (ENE2007−65541/ALT). Notes

The authors declare no competing financial interest. § Deceased.

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DEDICATION This work is dedicated to the late Prof. Xavier Esteve for his valuable insight. Professor Esteve was a great help to me in acquiring the fundamental knowledge and relevant engineering skills necessary to achieve the work conducted in this research.

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REFERENCES

(1) Davidson, W.; Erickson, D. New High Temperature Absorbent for Absorption Heat Pumps; ORNLORNL/Sub/85-22013/1; Oak Ridge National Laboratory: 1986. (2) Davidson, W.; Erickson, D. 260 °C Aqueous Absorption Working Pair Under Development. Newslett. IEA Heat Pump Cent. 1986, 4, 29− 31. (3) Ally, M. Simulated Performance of Absorption Heat Pumps Using a Mixed Aqueous Nitrate Working Fluid. ASME Winter Meeting, CONF-871234/ 87-WA/AES-2, 1987. (4) Ally, M. Thermodynamic Properties of Ternary Aqueous Solutions Relevant to Chemical Heat Pumps; Final Report, ORNL/TM-10258; Oak Ridge National Laboratory: 1987. (5) Howe, L.; Erickson, D. 260°C Absorption Working Pair Ready for Field Test. 4. Newslett. IEA Heat Pump Cent. 1990, 8, 7−9. (6) Ally, M.; Klatt, L.; Zaltash, A.; Linkous, R. Densities and Refractive Indexes of Aqueous (Lithium, Potassium, Sodium) Nitrate Mixtures. J. Chem. Eng. Data 1991, 36, 209−213. (7) Erickson, D.; Potnis, S. V.; Tang, J. Triple Effect Absorption Cycles. IECEC Int. Energy Convers. Eng. Conf. 1996, 2, 1072−1077. (8) Zaltash, A.; Ally, M. Predicting Viscosities of Aqueous Salt Mixtures. ASME Winter Annu. Meet. CONF-921110−30/DE 93002421, 1992. (9) Zhuo, C.; Machielsen, C. Performance of High-temperature Absorption Heat Transformers using Alkitrates as the Working Pair. 3. Appl. Therm. Eng. 1996, 16, 255−262. (10) Andersen, J.; Costa, A.; Ziegler, F. Measurements of Property Data for LiNO3, KNO3, NaNO3-H2O Mixture. Am. Soc. Mech. Eng., Adv. Energy Syst. AES 2000, 40, 21−26. G


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